You'll need to adjust the spotlight's angle to narrow the cone.  Be aware that you won't see any cone of light, but only the bright spot where the light hits solid objects.  If you want a cone of light, it is easiest to use a prop with a transparency map.

     Poser lights can do atmospheric effects, but it would be tough for a beginner to set up, and it will take longer to render.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5